Seagate 1.5TB hard drive shows only 500GB size

"I have downloaded SeaTools from http://www.seagate.com/www/en-us/support/downloads/seatools/seatooldreg (v2.13b (Graphical), ISO CD-ROM Image)
After booting the downloaded iso image, I have selected ""set drive capacity to MAX"" from the Advanced menu, and voilá, it works... the drive reports the expected size of 1.5TB again!

I'm still not happy though that something like this happens, and it would be still interesting to know why, and how could I avoid it."

"Sounds like a hardware fault.

First thing I would do is pull out the cable, plug it in to another machine and double check the BIOS.

If the other machine also reports 500GB, you have ruled out cable, power, socket / IC e.t.c.

Make sure there is no compatibility jumper (although I haven't seen one on many models for years). Just want to double check there is no conductive junk that has managed to cross anything!

If that doesn't work, I wouldn't bother checking for firmware updates - you don't want to start messing around with the other 15 drives to get them up to the same level. I would just email your retailer / wholesaler and get a RMA / replacement urgently."